The joining method mentioned at the outset is applicable, in particular, to the domain of motor vehicle engineering. In vehicle body construction, there is a requirement for fastening elements to be fastened to components such as metal sheets (vehicle-body sheets). In this case, such fastening elements frequently serve as an anchor for fastening further items, such as, for example, electrical lines and brake lines. Frequently, in such cases, a plastic clip is fitted on to the fastening element, the said items, in turn, then being affixed to the plastic clip. It is also possible for facing parts, carpets, fittings, etc. to be locked directly on to the fastening element.
Motor-vehicle bodies are traditionally produced from metal (sheet steel or aluminium). There is known in such cases, for the purpose of joining a fastening element in the form of a stud, the practice of using so-termed stud welding, in which opposing faces of the metal sheet and of the body panel are melted on to one another by means of an arc, and a material bond is then created between the metal sheet and the stud.
There is further known the practice whereby fastening elements made of a thermoplastic material are joined to thermoplastic components, the mutually opposing surfaces being melted on to one another and, likewise, a material bond ultimately being achieved.
However, there is also a requirement for fastening elements of a general nature to be joined to any surfaces, for example, to painted metal sheets, but also to glass-fibre reinforced plastic components or carbon-fibre reinforced plastic components. Since, in recent years, there has been an increasing trend towards motor-vehicle bodies of lightweight construction, there is increasing use of glass-fibre reinforced plastic components or carbon-fibre reinforced plastic components as body parts.
The adhesive bonding of fastening elements on to components is suitable for such general joining tasks. In such cases, an adhesive is applied to an adhesion face of the fastening element. The adhesive in this case is preferably of such a type that it is applied to the adhesion face in a kind of solid state, such that the fastening component, with the adhesive applied thereto, can be provided as bulk material or the like. This is of great importance for series production.
Such adhesives are brought to a viscous state by heating, such that, after the adhesion face has been placed on to the surface portion of the component, there can be created an adhesive bond that, after setting, lasts for the service life of the motor vehicle.
A joining appliance for fastening such components to a carrier face is known from the document DE 10 2004 012 786 A1. In that case, the component is realized as a stud having a shank portion and a flange portion, being so made from an inductively heatable material. The heating of the adhesive prior to the placing on to the carrier face is effected inductively, in that induction energy is introduced into the flange portion of the fastening element via an inductive field shaper, such that the fastening element and, indirectly thereby, also the adhesive applied thereto, becomes heated. After the fastening element has been applied to the carrier component, the supply of inductive energy is stopped, and the adhesive solidifies, in order to create the adhesive bond.
A further appliance for adhesive bonding of fastening elements to carrier faces is known from the document EP 1 250 391 B1, wherein the fastening elements are coated with a hot-melt adhesive that can be reactivated through the action of heat. Prior to the application to the carrier face, the adhesive is heated by means of hot air, the carrier face being heated at the same time. The heat supply is stopped after the fastening element has been placed on to the carrier face. Tacking of the fastening element on to the carrier face is achieved in this manner. How the subsequent final setting and final curing of the adhesive are effected, is not stated in this document. The adhesive bond obtained in that case is intended only to achieve a functional strength that enables the adhesive-bonded part to be conveyed without difficulty.
In large-scale series production, the time period required for executing the joining procedure is particularly important. Existing approaches to the execution of adhesion procedures frequently require a time period of two minutes or more. This is significantly longer than in the case of the stud welding mentioned at the outset, such that there is a need to reduce this time period.
Against the above background, it is the object of the invention to provide an improved joining method, an improved joining appliance and an improved fastening part.